Combustion of coal, oil, industrial waste, domestic waste, peat, etc. produces flue gases that may contain pollutants, such as dust particles, sulphur trioxide (SO3), etc. Pollutants, such as dust particles and sulphur trioxide, can also be produced as a residual product in gases formed in chemical processes, for instance in metallurgical processes. For removing dust particles from a gas it is common to employ an electrostatic precipitator. In the electrostatic precipitator the dust particles are charged by means of discharge electrodes. The charged dust particles are then collected on collecting electrode plates. The dust particles, and any other pollutants that have been collected on the collecting electrode plates, are then removed from the collecting electrode plates and transported away for further processing. For some processes, including processes where very fine dust particles and/or aerosols of, e.g., sulphur trioxide, are to be removed from a gas, a wet electrostatic precipitator is often employed. In a wet electrostatic precipitator a film in the form of a liquid, which is often water, is made to flow, continuously or at certain intervals, along the collecting electrode plates in order to clean the collecting electrode plates by removing the collected dust particles and any other pollutants therefrom. The use of a liquid for cleaning the collecting electrode plates has the advantage that a limited re-entrainment of collected pollutants occurs, as compared to that which occurs in “dry” electrostatic precipitators.
Patent Abstracts of Japan JP 06031202, filed in the name of Chubu Electric Power Co et. al., includes a description of an electrostatic precipitator, which has discharge electrodes and collecting electrodes. As described therein, the collecting electrodes are to be cleaned by means of water supply nozzles. These water supply nozzles spray water towards the collecting electrodes such that the collecting electrodes are cleaned by removing the collected dust particles therefrom. A problem with the electrostatic precipitator, which is described in the aforementioned JP 06031202 document, is that these water supply nozzles create small water droplets and/or aerosols, which in turn are entrained with the gas that is flowing through the electrostatic precipitator. Such water droplets and/or aerosols can cause corrosion problems in the equipment, such as the stacks, fans, reheaters, etc, which are located downstream of the electrostatic precipitator. Also, such water droplets and/or aerosols may in addition cause the emission of dust particles, due to the fact that such entrained water droplets and/or aerosols, in addition to the liquid, may also contain dust particles and dissolved chemicals.